Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Cameras have become ubiquitous when it comes to recording images. Various cameras may record images on film or digitally store images as a series of bits within a computer memory (e.g., a hard drive). Many devices even have cameras integrated in them. For example, mobile phones, tablets, and laptop computers may include cameras.
One application for cameras is in the field of computer vision. In computer vision, in order to make inferences from recorded images, calibrating the camera recording the images can be important. Such a calibration can provide a correlation of the appearance of a recorded image to the spatial layout of a physical scene. Further, calibration can correct for defects in the fabrication and/or assembly of a camera sensor/lens used to record images. For example, if an aperture of a camera is off-center with respect to a camera sensor, a calibration may account for this (e.g., using a processor that provides a correction to recorded images such that they more accurately reflect a physical scene).
One method of calibrating cameras includes applying the pinhole camera model. The pinhole camera model assumes the camera being calibrated is an ideal pinhole camera (i.e., a camera with no lenses and a point-like aperture). Using the pinhole camera model approximation, the coordinates (e.g., in three-dimensions) of a physical scene may be mapped to a projection on a two-dimensional plane, where the projection on the two-dimensional plane is represented by a recorded calibration image. The location of the pinhole aperture in the theoretical pinhole camera can be determined based on the calibration image. Other parameters of the theoretical pinhole camera can also be determined (e.g., focal length). If the location of the pinhole aperture is not centered with respect to the camera sensor, steps can be taken to account for the off-center location of the aperture. Determining the location of the pinhole aperture and accounting for it may include calculating one or more elements of a camera matrix based on one or more calibration images.
Other methods of calibration can be employed to correct for other defects inherent in optical design or due to fabrication/assembly, as well. For example, one or more distortion coefficients can be calculated based on a recorded calibration image. The distortion coefficient may be used to account for optical non-uniformities arising due to a lens in the camera (e.g., barrel distortions, mustache distortions, or pincushion distortions). In additional, other optical aberrations can be accounted for using calibration (e.g., defocusing, tilting, spherical aberrations, astigmatism, coma, or chromatic aberrations).